There has been conventionally known a method for manufacturing two bearing rings (ring-shaped members), which are an inner ring and an outer ring for a rolling bearing, from one column-shaped material (so-called parent-child taking) (for example, see PTL 1). This manufacturing method includes the following first step to fifth step.
First step: through upsetting in hot working, a disk-shaped intermediate formed product 202 having an arc-shaped generating line of an outer circumferential surface illustrated in (b) of FIG. 14 is formed from a column-shaped material 201 illustrated in (a) of FIG. 14.
Second step: through closed die forging, a stepped cylindrically-shaped formed product 203 illustrated in (c) of FIG. 14 is formed from the intermediate formed product 202. In this formed product 203, an outer periphery on one end of a small-diameter inner ring 205 is coupled to an inner periphery on one end of a large-diameter outer ring 204. A bottom 206 is formed on an inner periphery on the other end of the inner ring 205.
Third step: the formed product 203 is cut at the coupled site of the outer ring 204 and the inner ring 205 to separate the formed product 203 into the outer ring 204 and the inner ring 205 as illustrated in (d) of FIG. 14.
Fourth step: as illustrated in (e) of FIG. 14, the bottom 206 is punched from the separated inner ring 205.
Fifth step: the outer ring 204 and the inner ring 205 are formed into a predetermined shape by a rolling process.
PTL 2 discloses the method of producing a ring-shaped member. In this method, a large-diameter cylindrical member and a small-diameter cylindrical member before cold rolling are made to have identical weights, and only the small-diameter cylindrical member is cold-rolled. Thus, the method produces a ring-shaped member with a diameter and a shape identical to those of the large-diameter cylindrical member (Since the large-diameter cylindrical member is not to be rolled, the large-diameter cylindrical member becomes the ring-shaped member without change).
The above-described PTL 1 discloses the method of producing a large-diameter cylindrical member and a small-diameter cylindrical member by a single forging process. The small-diameter cylindrical member is upset, and is then subject to a rolling process. Thus, in the method, the large-diameter cylindrical member in forging is produced to be a ring-shaped member serving as an inner ring, and the small-diameter cylindrical member in the forging is produced to be the ring-shaped member serving as an outer ring.